Replace the OTEL-based tracing layer with tracing based layers

crates/tower/src/utils.rs

@@ -0,0 +1,33 @@
+// Copyright 2023 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use opentelemetry::{KeyValue, Value};
+
+/// A simple static key-value pair.
+#[derive(Clone, Debug)]
+pub struct KV<V>(pub &'static str, pub V);
+
+impl<V> From<KV<V>> for KeyValue
+where
+    V: Into<Value>,
+{
+    fn from(value: KV<V>) -> Self {
+        Self::new(value.0, value.1.into())
+    }
+}
+
+/// A wrapper around a function that can be used to generate a key-value pair,
+/// make or enrich spans.
+#[derive(Clone, Debug)]
+pub struct FnWrapper<F>(pub F);